Field of the Invention
The invention relates to a method and a device for detecting the quality of fuel for an internal combustion engine.
Fuels for internal combustion engines consist of a mixture of hydrocarbon compounds that may contain additions of oxygen-containing organic components and additives in order to improve the properties.
The proportions of the various hydrocarbons in the fuel result in different effects on the operating performance of the internal combustion engine; in particular, starting performance, smooth running, output, fuel consumption, acoustics and exhaust emissions are influenced. Modern internal combustion engines have to be able to process fuels of varying quality without the operating performance being noticeably impaired.
The quality of the fuel that is fed to an internal combustion engine therefore has a significant influence on the combustion operation and on the exhaust emissions, in particular during a cold start of the internal combustion engine.
Currently, changes in the quality of fuel are detected with the aid of what is known as a starting mix adaptation or the lack-of-smoothness method and are compensated for by changing the injection times. In the known methods, an increase in speed when the internal combustion engine is started or the fluctuations in the speed when the engine is being started is evaluated. If the increase in speed or the fluctuations in speed do not lie within a permitted, predetermined confidence interval, the injection time is corrected accordingly. However, the extent of correction is calculated relatively inaccurately, and consequently under certain circumstances the correction will be excessive. Particularly in the case of what is known as a xe2x80x9cbad startxe2x80x9d, the injection time is changed in such a manner that the fuel/air mix becomes richer, and consequently the fuel/air mix can become too rich after refueling with a very good quality of fuel. The internal combustion engine will then only start with difficulty or will no longer start at all. Furthermore, there is a risk of the undesired speed characteristics having been caused not by a changed quality of fuel, but rather by other fault sources.
Published, Non-Prosecuted German Patent Application DE 40 27 947 A1 has described various methods that can be used to take account of changes in the fuel quality. First of all, each time the vehicle driven by the internal combustion engine is refueled, the control deviation can be measured in the lambda control circuit and an adaptation value can be adjusted in such a way that the determined control deviation disappears. The method has the drawback that it only works when the lambda control is active, which, however, is not the case in particular in the case of cold internal combustion engines. Second, methods have been proposed which ensure that the internal combustion engine is able to operate even when cold if the fuel composition changes significantly during refueling, for example as a result of a tank which contains fuel having been run almost to empty, followed by refueling with a fuel which contains predominantly methanol. The tank levels before and after refueling and the data available on commercially available fuels are used to estimate what fuel compositions could be present. The pilot control values are then changed for operation of the internal combustion engine with fuels of the possible compositions, and checks are carried out on the basis of the composition with which the internal combustion engine runs best. The values are then used to control the internal combustion engine further.
It is accordingly an object of the invention to provide a method and a device for detecting the quality of fuel for an internal combustion engine that overcomes the above-mentioned disadvantages of the prior art devices and methods of this general type, which can be used to detect the quality of the fuel which is to be supplied for combustion to an internal combustion engine in a simple and inexpensive way.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for detecting a quality of a fuel supplied to an internal combustion engine. The method includes directing onto a temperature sensor at least some of the fuel injected by an injection valve into an induction pipe of an intake port of the internal combustion engine so that a wall film is formed around the temperature sensor; determining a reduction in temperature that occurs as a result of an enthalpy of vaporization; and determining the quality of the fuel from the reduction in temperature.
Installing the temperature sensor in the induction pipe of the internal combustion engine in such a manner that at least some of the fuel jets from the injection valve is sprayed onto it allows a wall film to form around the temperature sensor. The reduction in temperature that occurs as a result of the enthalpy of vaporization at the temperature sensor is measured and is used as a criterion for the quality of the fuel supplied to the internal combustion engine.
With the aid of this information, it is possible to formulate a change in the injection time exclusively or in addition to the adaptation of the starting quantity or the lack-of-smoothness method.
The method according to the invention or the device has the advantage that the quality of fuel used can in a simple way be recorded very quickly by measurement technology, immediately after the first injections of fuel after the internal combustion engine has been started. There is no need for any values to be stored in the control unit, so that it is possible to rule out complications resulting from refueling operations and changes in fuel quality.
The quantity of the wall film in the induction pipe can also be determined by measurement technology during ongoing operation and in the event of dynamic load states, so that the lambda window for the lambda control can be reduced. The quantity of fuel that can be applied in the time before the lambda control is active can be reduced by reliable detection of the fuel quality. As a result, the emissions of HC and CO decrease.
The use of a temperature sensor disposed in the fuel jet makes it possible to estimate the fuel temperature, with the result that further engine management improvements and diagnoses, such as the diagnosis of an evaporation retention system and an exhaust gas recirculation system, are assisted. Moreover, as a result the filling can be calculated more accurately in what is known as an induction-pipe filling model.
The signal from the temperature sensor can also be used for diagnosis of the injection valve. A defective injection valve can easily be detected by a plausibility test carried out on the signal output from the internal combustion engine control unit for opening the nozzle of the injection valve and on the signal from the temperature sensor. If there is an activation signal for the injection valve and the signal at the temperature sensor does not change, it is possible to conclude that no fuel has reached the temperature sensor and therefore no fuel has been injected. The reason for this may, for example, lie in a closed, jammed injection valve. The fault can be input into a fault memory and/or indicated to the driver.
In accordance with an added mode of the invention, there is the step of using values of the reduction in temperature as input variables for a characteristic diagram in which associated values for a correction factor are stored. The correction factor is taken into account in a calculation of an injection time of the internal combustion engine.
In accordance with an additional mode of the invention, there is the step of obtaining the reduction in temperature by comparing a first temperature in the intake port of the internal combustion engine and a second temperature at the temperature sensor after the fuel has been injected.
In accordance with a further mode of the invention, there is the step of measuring the first temperature in the intake port of the internal combustion engine using a further temperature sensor.
In accordance with another mode of the invention, there is the step of measuring the first temperature in the intake port before the internal combustion engine is started; measuring the second temperature using the temperature sensor after injection has taken place; calculating the reduction in temperature from a difference between the first temperature and the second temperature; and reading-out the associated values for the correction factor from the characteristic diagram in dependence on the values for the reduction in the temperature and a time since the internal combustion engine was started.
In accordance with another added mode of the invention, during steady-state operation of the internal combustion engine, the first temperature in the intake port is measured. The second temperature is measured using the temperature sensor after injection has taken place. The reduction in temperature is calculated from a difference between the first temperature and the second temperature, and the associated values for the correction factor are read-out from the characteristic diagram in dependence on the reduction in temperature and a load on the internal combustion engine.
With the foregoing and other objects in view there is provided, in accordance with the invention, a device for detecting a quality of fuel supplied to the internal combustion engine. The engine has an intake port with an induction pipe, and the induction pipe is assigned an injection valve for injecting fuel, so that the fuel can be injected into the induction pipe. The device contains a temperature sensor disposed in the induction pipe, in such a manner that while the fuel is being injected, at least some of the fuel strikes said temperature sensor.
In accordance with an added feature of the invention, the internal combustion engine is a multi-cylinder internal combustion engine having a plurality of induction pipes corresponding to a number of injection valves, and the temperature sensor is one of a plurality of temperature sensors with a respective one of the temperature sensors disposed in each of the induction pipes.
In accordance with another feature of the invention, the internal combustion engine is a multi-cylinder internal combustion engine-having a plurality of induction pipes corresponding to a number of injection valves, and the temperature sensor is disposed in only one of the induction pipes.
In accordance with another feature of the invention, the injection valve and the temperature sensor are combined to form a structural unit.
In accordance with a further feature of the invention, the injection valve has a holder which extends in a direction of a fuel jet from the injection valve and is angled off at a free end, to which the temperature sensor is secured.
In accordance with a concomitant feature of the invention, connection lines are provided functioning as common connection lines connected to both the injection valve and the temperature sensor.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and a device for detecting the quality of fuel for an internal combustion engine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.